1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly, to wiring technology for the driving wires of piezoelectric elements provided in a liquid ejection head.
2. Description of the Related Art
An inkjet type image forming apparatus has a print head in which a plurality of nozzles (ejection ports) are arranged in the form of a matrix, and it forms an image on a recording medium by ejecting ink droplets from the nozzles onto the recording medium.
In a print head of the related art, as shown in FIG. 28, ink is supplied to a pressure chamber 52 from a common liquid chamber 55 disposed on the same side of the pressure chamber 52 as the side where the nozzle 51 is formed in the pressure chamber 52. When an electrical signal corresponding to the image data is supplied to a piezoelectric element 58 located on a diaphragm 56, the diaphragm 56 is deformed by the driving of the piezoelectric element 58. Consequently, the volume of the pressure chamber 52 is reduced, an ink droplet is ejected from the nozzle 51, and this ink droplet lands on a recording medium, thereby forming a dot on the recording medium. By combining dots of this kind, an image is formed on the recording medium.
In recent years, there have been demands for improved image quality in image forming apparatuses. In order to achieve higher image quality, it is necessary to arrange the nozzles of the print head at high density, thereby obtaining a high number of pixels per image. Therefore, various technologies have been proposed with the aim of increasing nozzle density (see, for example, Japanese Patent Application Publication Nos. 9-226114; 2001-179973, 2000-127379, 2000-289201 and 2003-512211).
Japanese Patent Application Publication No. 9-226114 discloses a print head in which piezoelectric elements are disposed on a diaphragm which forms the ceiling of pressure chambers, a reservoir (common liquid chamber) is provided on the side of the diaphragm adjacent to the piezoelectric elements, and holes for supplying ink are provided in the diaphragm.
Japanese Patent Application Publication No. 2001-179973 discloses a print head in which piezoelectric bodies (piezoelectric elements) are disposed on a diaphragm which forms the ceiling of pressure chambers, and an ink supply tank (common liquid chamber) is provided on top of the piezoelectric bodies, via a partition.
Japanese Patent Application Publication No. 2000-127379 discloses a print head in which a reservoir (common liquid chamber) is formed on the same side as piezoelectric elements, which are disposed on the opposite surface of pressure generating chambers (pressure chambers) from the nozzle side.
Japanese Patent Application Publication No. 2000-289201 discloses a print head in which piezoelectric actuators (piezoelectric elements) and a common ink chamber (common liquid chamber) are disposed on the same side of pressure chambers as the nozzles, and a substrate (wiring layer) is disposed on the opposite surface of the pressure chambers to the nozzles.
Japanese Patent Application Publication No. 2003-512211 discloses a print head in which an ink supply layer formed by a porous member for supplying ink to pressure chambers is disposed between a nozzle layer in which nozzles are formed, and a cavity layer formed with ink cavities (pressure chambers). According to this patent, piezoelectric elements are disposed on a displacement plate (diaphragm) which constitutes the ceiling of the ink cavities, wiring members are provided from the piezoelectric elements in a substantially perpendicular direction with respect to the nozzle surface, and a substrate (wiring layer) is disposed at the ends of these wiring members.
In the print head shown in FIG. 28, the supply ports (flow channels) which connect the common liquid chamber with the pressure chambers have a complex structure, and if ink of high-viscosity is used, then refilling characteristics in respect of the supply of ink to the pressure chambers after ejection of ink are poor.
In the print heads disclosed in Japanese Patent Application Publication Nos. 9-226114 and 2001-179973, since the driving wires for the piezoelectric elements are located on the diaphragm, it is not possible to ensure sufficient space for the driving wires, and it becomes difficult to dispose the nozzles at high density.
In the print head disclosed in Japanese Patent Application Publication No. 2000-127379, the driving wires to the piezoelectric elements are formed by wire bonding or film deposition, and they are connected to external wires installed above the common liquid chamber. However, since the driving wires are formed externally to the common liquid chamber, it is difficult to ensure space for the driving wires of the piezoelectric elements, and hence there are restrictions on the size of the common liquid chamber. If the common liquid chamber is small in size, then ink supply to the pressure chambers cannot meet demand, and it becomes difficult to drive the nozzles at high frequency. Furthermore, the print head disclosed in Japanese Patent Application Publication No. 2000-127379 only contemplates the composition of a print head having one nozzle row, and it is not suitable for a composition in which a plurality of nozzles are arranged at high density.
In Japanese Patent Application Publication No. 2000-289201, driving wires (aluminum plugs) connecting the piezoelectric elements with the wiring layer are formed in such a manner that they pass through a laminated plate between the piezoelectric elements and the wiring layer, which are disposed in such a manner that the pressure chambers are sandwiched therebetween. Therefore, it is difficult to ensure sufficient space for the driving wires, and hence the nozzles cannot be formed to high density.
In the print head disclosed in Japanese Patent Application Publication No. 2003-512211, a common liquid chamber (ink manifold) for accumulating ink to be supplied to the ink supply layer is provided on the opposite side of the wiring layer with respect to the wiring layer. Therefore, the flow channel for supplying ink to the pressure chambers from the common liquid chamber and via the ink supply layer is long, the supply of ink from the common liquid chamber to the pressure chambers is not sufficiently rapid, and it is difficult to form the nozzles at a high density. Moreover, if the nozzles are driven at high density, the ink supply will not be able to keep up with demand. Moreover, since the ink supply layer is constituted by a porous member, the print head is not suitable for ejection of high-viscosity ink.